Metal-clad plate type rheostat



* 1950 G. L. MGFARLAND, JR, ETAL 2,493,500

METAL GLAD PLATE TYPE RHEOSTAT Filed 00b. 21, 1948 To BE FILLED HITHcnsrms CEMENT ni a: mun HIT/l CAST/N6 I Inventor-s: 1* Gem" eL.PlFar-landJr.-,

Ernest E Goetz,

by w

4 Their Attorneg.

Patented Feb. 21, 1950 UNITED STATES PATENT OFFICE METAL-GLAD PLATE TYPERHEOSTAT George L. McFarland, Jr., and Ernest F. Goetz,

Schenectady, N. Y., assignors to General Electric Company, a corporationof New York Application October 21, 1948, Serial N0. 55,702

5 Claims. 1

This invention relates to improvements in rheostats, and moreparticularly to metal clad plate type rheostats.

Demand for this type of rheostat has resulted in continual research bymanufacturers and others to provide improvements which will increase thelife of such rheostats; reduce the manufacturing cost; minimize themounting space required; and increase the wattage rating for a givensize of rheostat.

It is an object of this invention to provide a rheostat in whichimprovements as outlined above are obtained.

These and additional objects not outlined above will be apparent tothose skilled in the art from a consideration of the followingspecification and the accompanying drawing, wherein Fig. 1 is a planview of a rheostat embodying our invention, with a section of the coverbroken away; Fig. 1a is a cross sectional view taken on line IaIa ofFig. 1; Fig. 2 is a cross sectional view of a portion of the rheostattaken on line 2- 2 of Fig. 1; Fig. 3 is a cross sectional view of aportion of the rheostat taken on line 3-3 of Fig. 1; Fig. 4 is a crosssectional view taken on line 44 of Fig. 1; Fig. 5 is a cross sectionalview of a "portion of the rheostat taken on line 55 of Fig. 4; and Fig.6 is an enlargement of a portion of the cross sectional view shown inFig. 4.

Referring to the drawing, Fig. 1 shows the operating side of a rheostatI illustrative of one form of this invention. This rheostat includes acircular wiring plate 2 which is made of suitable insulating materialand has a projection 3 extending radially beyond the periphery of theplate. Mounted on wiring plate 2 are U-shaped resistance elements 4having legs 4a and 42). Legs 4a are approximately radially disposed onthe operating face of wiring plate 2 and terminate opposite a ring ofapertures 5 in the wiring plate. Legs 4b are similarly disposed on theopposite face of the wiring plate 2. However, with respect to eachresistance element 4, leg 4a terminates at aperture 5 next following theaperture 5 at which leg 42) terminates. L-shaped contacts 6, each havingone long and one short arm are positioned with the short arms projectingthrough the apertures 5 and the long arm 2 of the contacts 6. A briefglance at Fig. 4 will show these elements in further detail.

Terminals 8 and 9 are moulded into the projection 3 of the wiring plate2, and are electrically connected, respectively, to the first and lastof the contacts 5 by conducting strips I0 and I I. A terminal I2 islikewise moulded into the projection 3 of the wiring plate 2 and islocated between terminals 8 and 9. The terminal I2 is electricallyconnected to a collector ring (to be described later) by a conductorstrip I3.

To show the manner in which terminal 8 is connected to the first ofcontacts 6 of the series circuit, Fig. 2, is provided. This crosssectional view taken on line 2--2 of Fig. 1 shows contact strip Illconnected between terminal 8 and the bent portion of the first ofcontacts 6. Leg 417 of the first of resistance elements 4 is connectedto the end of the short arm of the same contact 6.

To show the manner in which the terminal 9 is connected to the last ofcontacts 6 of the series circuit Fig. 3 is provided. This crosssectional view, taken on line 3-3 of Fig. 1, shows contact strip IIconnected between terminal 9 and the end of the short arm of the last ofcontacts 6. Leg 4a of the last of the resistance elements 4 is connectedto the bent portion of the same contact.

To show the operating means and further structural detail of therheostat a cross sectional vieW on line 4-4 of Fig. 1 is shown in Fig.4. This view shows that the rheostat is provided with a circular bearinghub I4. Bearing hub I4 is made of suitable insulating material, iscentrally located on the operating side of the rheostat I, and servesseveral functions which I shall now describe.

First, the inner face of the bearing hub I4 is recessed to provide anannular surface I4a which presses against the longer arm of the L-shapedcontacts 6 and holds the contacts in position against the inner face 2aof the wiring plate 2. The bearing hub is itself secured by a metalliccover plate I5 which has an aperture I5a of suflicient size to pass overthe projecting portion I4b of the bearing hub I4 and allows the coverplate l5 to press against the flanged portion I40 of the bearing hub I4.A similar cover plate I 6 rests against flanged surface 2b of, thewiring plate 2 on the other side of the rheostat from the operating sideand the corners I! of the two plates I5 and I6 are flattened and weldedtogether as shown in Fig. 1A. In this manner the bearing hub I4 issecured in the rheostat and the contacts 6 are held between adjacentsurfaces of the wiring plate 2 and the bearing hub I4.

In bearing hub I4, an aperture I8 is also pro vided into which abushing20 (shown in Figs. 4, 5 and 6) ismolded as an insert and receivesan-operating shaft IS. The portion I9a of the shaft I9 is of reducedcross section, threaded at its end, and has two flat sides 19b and H30,(best seen in Fig. 6). Side I9c is slightly tapered so that the portion[9a of the shaft I 9 has a dimine ishing cross section in the directionof its threaded end.

We provide a brush housing 2i having a metal insert plate 22approximately rectan ular in shape moulded thereinto. Insert plate 22 isperpendicular to the aXis of the. Operating Shaft 19 when the brushhousing 2| is assembled on portion l9a of shaft l9, and has a centralaperture 22a to conform approximately to the cross section of [9a inorder that the insert plate 22 carrying the brush housing 2! may beforced on the portion 19a of the shaft 19 by a lock washer 23 and nut24. As so assembled there is no play between the portion {9a. of theshaft and the metal insert plate 22 because any clcaranceswhichmightbepresent are taken up. by thetaper of the face l9c of the shaft.When forced onthe shaft by thegnut 24, the insert plate 22 comes to restagainst an abutment 19d formed by the reduction inscross section of theportion I9a .Of the shaft. A n L-shaped operating handle .25 is, securedto the.- other end of the operating shaft 89 and the small arm 25a. ofhandle 25' rides in a groove Me in the operating face of the bearing hub14. The inner surface of the longer arm 25?) of the L- shaped handleabuts againstthe end of bearing 20. Thus shaft I 9 supports the brushhousing 2! which rotates with shaft H) as the; latter is turned by meansof the operating handle 25.

Bearing hub I4 is also provided with an annular flange Md adapted tosupporta collector ring 26. The collector ring; 26 is biased to restagainst flange Md by-a collector brush 2]- which is brazed to a brushsupport. 28. A contact brush 2.9 is also brazed to-the brush support 28at a point diametrically eppos-ite. to brush 21- and is biased to rideonthe contacts 6 as the shaft. [-9 is rotated. Me n f r iasingbrushes 2 an2-9,. comprises twousprings 3 9 and 31 which are secured respectivelyindiametrically opposed recesses 39a and 3H1- in the inner face.- of thebrush. housin 2!. Both springs 3t andsl, are secured to the brushsupport 23 by any suitable means. The. operatingshaft 1&9 is thus.adequately insuIatedfIom the electrical circuits by the bearing hub 14and the brush housing 2-]. Also the brushes are easily.- han ed y implyremoving he brush housin 2!. Furthermore, the springs 33 and 31 cannotbe lost during this operation since they are secured to both theybrushzsupport: 28' and the, brush housing 2!.

In reviewing thefunctions of the bearing hub l4, it is seen. that hub Mserves to hold the L- shaped contacts Bin place against the inner face2a of the wiring plate 2; further,v bearing hub l4 provides an apertureto receive the bearing 20 which in turn, secures the operating shaft 19on which are mounted the operating handle 2-5. and the brush contactmeans; and bearing hub I4. also provides a seat to. support thecollector ring- 2.6-. A further function of the bearinghub M, will bediscussed later in-relation to, adjustable stops to be described indetail.

a d in.- securing con a s 6., o uctor strip i3, and resistance elements.i, and to provide furtherinsulation and protection for these-membars, acasting cement is poured intothe portion of, the. rheostat between theplates: andlt as indicated in Fig. 4. When this mixture has, hardenedit, provides insulation and a firm. suppor for t ese element and iitself protected fr mdama ey the cover plates l5 and; it.

To enable the operator to set the voltage or speed of his machineadjustable stops in the form of identical circular plates 32 and 33 areprovided and are positioned as-shown in Figs. 1 and 4. Referring to Fig.4 it will be seen that both plates are centrally apertured to permitbearing 29 to pass through the. apertures as the plates are secured tothe operating face of bearing hub M.

Fig. 1 shows that the diameter of the plates is made approximately equalto the diameter of the internal edge of groove Me to permit the smallarm 25a of, the L-shaped handle 25 to ride in groove Me. Plates 32 and33 are provided with projections 32a and 33a which overlap the groove Meand lie in the path of the small arm 25 of the operating handle 25. Theposition-of these projections may be adjusted -toprovide stops for thehandle 25 by means of arcuately shaped slots 32b and 331) through whichcap screws 34 are inserted to secure the plates 32 and 33 to the face ofbearing hub M. Once the projections'32a and 33a. are set in a particularposition byrotating the plates 32 and 33 with respect to the bearing hubI 4 the cap screws 94 may then be tightened to secure the platesin theselected positions and thus provide two stops for the rotation of theoperating handle 25.

To provide a means for mounting the rheostat the flattened and weldedcorners H of the covers 15 and 16 are apertured as at Ila.

The rheostat as illustrated and described herein has an appreciableadvantage in wattage rating over conventional rheostats now in use. Asan example, in contrast to a conventional rheostat. of a size presentlymanufactured, our rheostat of similar size has a rating of approximatelythree time that of the conventional rheostat. This. increase in wattageis due to the fact that the level of temperature in the entire rheostat.may be raised. approximately 50 higher than that of conventionalrheostats without destroying the utility of the, rheostat. This highertemperature is made possible in part by they use of metal coverswhichjhcld. thev structure mountin p1ates together and in operable formeven though the cement or wiring plate is cracked by heat. It is alsodue in part to a balance of temperature resulting from the use ofU-shaped resistance elements'having one leg on each side of the wiringplate, so that the heat is not concentrated on one side. It is furtherfacilitated by the use of the metal covers and the casting cementwherein thecasting cement conducts the heat to the metal covers whichtend to spread the temperature more evently and also conduct the heataway through the flattened and welded mounting corners.

Use of the flattened and welded mounting corners also provides anadvantage in lowering the cost of production and minimizing mountingspace, as contrasted with the conventional'meth- 0d of securing mountinglegs to the rheostat.

Although an exemplary form of the invention has been shown in theaccompanying drawings and described herein in detail, itis to beunderstood that the, disclosures are not: intended to be restrictive butthat each may embody various modifications detail structure-without.departing from the spirit, of the invention or the scope of; theappended claims.

What; we claim as newand desire to secure by Letters Patent of theUnited States is:

l... A. plate typ rh ostat comprisin a mountin 'plate having a; firstcentral. aperturaan outer ring iii-approximately radially disposed:resist-- ance elements mounted thereon, an inner ring of radiallydisposed contacts electrically connected to said resistance elements andforming a series circuit of said elements, said contacts lying against aface of said plate and projecting into said first central aperture,terminal means for said series circuit, a dielectric bearing hub havinga second central aperture, said hub overlying said first centralaperture and an inner peripheral portion of said mounting plate andlying against said ring of radial contacts thereby to press saidcontacts against the face of said mounting plate and. to hold saidcontacts in alignment, a contact ring centrally mounted upon saidbearing hub and radially inwardly spaced from said ring of contacts,terminal means for said contact ring, a cover plate overlying saidmounting plate and a peripheral portion of said hub to hold saidmounting plate and said bub together, an operating shaft mounted in thecentral aperture of said hub, and a pair of angularly spacedelectrically connected brushes mounted upon said. shaft and engagingsaid ring and said contacts respectively.

2. A plate type rheostat comprising a circular mounting plate having afirst circular central aperture, an outer ring of approximately radiallydisposed resistance elements mounted thereon, an inner ring of radiallydisposed contacts electrically connected to said resistance elements andforming a series circuit of said elements, said contacts lying against aface of said plate and projecting into said first central aperture,terminal means for said series circuit, a dielectric bearing hub havinga second central aperture, said hub overlying said first centralaperture and an inner peripheral portion of said mounting plate andlying against said ring of radial contacts thereby to press saidcontacts against the face of said mounting plate and to hold saidcontacts in alignment, a contact ring centrally mounted upon saidbearing hub and radially inwardly spaced from said ring of contacts,terminal means for said contact ring, a pair of substantiallyrectangular metallic cover plates disposed on opposite sides of saidmounting plate, one of said cover plates overlying a peripheral portionof said hub to hold said mounting plate and hub together and said coverplates being flattened and connected together at their corners andapertured to form a mounting means for said rheostat, an operating shaftmounted in the central aperture of said hub, and a pair of angularlyspaced electrically connected brushes mounted upon said shaft andengaging said ring and said contacts respectively.

3. A plate type rheostat comprising a circular plate having a contactaperture, an outer ring of approximately radially disposed resistanceelements mounted thereon, an inner ring of radially disposed contactselectrically connected to said resistance elements and forming a seriescircuit of said elements, said contacts projecting into said aperture,terminal means for said series circuit, a contact ring centrallydisposed in said aperture and having terminal means, a dielectricbearing hub arranged to press said contacts against a face of said plateand to maintain said contacts in position, said bearing hub having acentral aperture, a metallic cover arranged to maintain said plate andsaid bearing hub in fixed position relative to each other,

an operating shaft mounted in the aperture of said hub, a dielectricbrush support secured to one end of said operating shaft, and springbiased contact brushes in said brush support, one of said brushesengaging said ring of radially disposed contacts and the other of saidbrushes engaging said contact ring.

l. A plate type rheostat comprising a circular piate having a centralaperture, an outer ring of approximately radially disposed resistanceelements mounted thereon, an inner ring of radially disposed contactselectrically connected to said resistance elements and forming a seriescircuit of said elements, said contacts projecting into the aperture,terminal means for said series circuit, a contact ring centrallydisposed in said aperture and having terminal means, a dielectricbearing hub arranged to press said contacts against a face of said plateand to maintain said contacts in position, said bearing hub having acentral aperture, a metallic cover arranged to maintain said plate andsaid bearing hub in fixed position relative to each other, an operat ingshaft mounted in the aperture of said hub, said cover being flattened atits corners and apertured to form a mounting means for said rheostat, adielectric brush support secured to one end of said operating shaft, andspring biased brushes in said brush support, one of said brushesengaging said ring of radially disposed contacts, and the other of saidbrushes engaging said contact ring.

5. A plate type rheostat comprising a circular plate having a centralaperture, an outer ring of approximately radially disposed resistanceelements mounted thereon, an inner ring of radially disposed contactselectrically connected to said resistance elements and forming a seriescircuit of said elements, said contacts projecting into said aperture,terminal means for said series circuit, a contact ring centrallydisposed in said aperture and having terminal means, a dielectricbearing hub arranged to press said contacts against a face of said plateand to maintain said contacts in position, said bearing hub having acentral aperture, a metallic cover adapted to maintain said plate andsaid bearing hub in fixed position relative to each other, an operatingshaft mounted in the aperture of said hub, said cover being flattened atits corners and apertured to form a mounting means for said rheostat, adielectric brush support secured to one end of said operating shaft,spring biased brushes in said brush support, one of said brushes ridingon said ring of radially disposed contacts and the other riding on saidcontact ring, said metallic cover being filled with casting cement.

GEORGE L. McFARLAND, JR. ERNEST F. GOETZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 687,044 Mackintosh Nov. 19, 1901689,445 Wirt Dec. 24, 1901 2,303,499 Rich Dec. 1, 1942 2,312,110McFarland, Jr. Feb. 23, 1943

